1. Field
The present disclosure relates generally to the field of retaining walls and, more specifically, to retaining wall blocks and techniques for manufacturing retaining wall blocks.
2. Background Information
Retaining walls are widely used in a variety of landscaping applications. Typically, they are used to maximize or create level areas and also to reduce erosion and slumping. They may also be used in a purely decorative manner. In the past, retaining wall construction was labor intensive and often required the skills of trained tradespeople such as masons and carpenters. More recently, retaining wall construction has become significantly simplified with the introduction of self-aligning, modular, molded blocks of concrete that may be stacked in courses without the use of mortar or extensive training. With these types of retaining wall blocks, it is possible to erect a retaining wall quickly and economically, and the finished product creates the impression and appearance of a conventional block-and-mortar retaining wall.
The feature that allows the foregoing blocks to be so easily and precisely assembled is the interconnection between adjacent courses of blocks. Typically, each retaining wall block will include a projection and a recess located at oppositely facing surfaces, such as a top surface and a bottom surface, for example. The projection and recess are complementarily shaped, with the projection protruding beyond the top (or bottom) surface of the block with the recess extending inwardly from the bottom (or top) surface of the block. In use, a projection of a first block is received within the recess of a second block to interconnect and position the blocks adjacent each other in a predetermined relation. With a plurality of blocks, such interconnections make it possible to lay courses of blocks in an accurate and expedient manner. Moreover, such an assembled retaining wall is able to resist lateral forces exerted by the material being retained and reduce bowing. Blocks having these interconnections are usually the same size and may be assembled in a coplanar arrangement in only a simple, running bond pattern. In a variation of the aforementioned blocks, the projection and recess may be arranged so that adjacent courses are offset a predetermined amount. With this type of retaining wall block, each successive course may be offset from the preceding course by the same amount so that the assembled wall is skewed at a predetermined angle from the vertical. These blocks also have the dimensions to enable them to be set in only a simple running bond pattern.
A recent development in mortarless retaining walls has been the advent of blended pattern retaining walls. These walls differ from the aforementioned walls in that the preformed blocks used to construct a retaining wall are differently sized. This feature allows retaining walls to be assembled in a variety of patterns and bonds. Usually, these types of preformed blocks are horizontally and vertically oriented and have dimensions that are based upon an incremental unit such as the thickness of a horizontal, preformed block. For example, the thickness of a horizontal block is one increment and the height of a vertical block is two increments. With these types of preformed blocks, it is possible to construct a retaining wall with no discernable courses. A drawback of this type conventional mortarless retaining walls is that setbacks are not possible and the assembled retaining wall must be substantially vertical.
In an attempt to overcome the foregoing drawback with conventional mortarless retaining walls, a retaining wall may be arranged in thick courses, and the blocks within these thick courses may be randomly arranged. For example, a course may be two incremental units high within which the differently dimensioned preformed blocks are arranged. Alternatively, the course may be three incremental units high within which the differently dimensioned preformed blocks are arranged. There are several drawbacks with this type of wall. One drawback is that the vertical blocks dictate the height of the course. Thus, if vertical blocks are used, each entire course must be coplanar and all of the blocks must lie in the same plane. Otherwise, the projections of blocks in one course would not be able to be received within the recesses in blocks of another course, and the interconnection would be defeated. Another drawback with this type of retaining wall is that the number of arrangements available within each course is limited, and a truly random arrangement is not possible.
Another drawback with the foregoing conventional mortarless retaining walls is that the front faces of the finished blocks forming the retaining walls are typically not provided with an attractive finished appearance, and often require covering or painting before or after installation to form the retaining walls.
Moreover, low slump masonry concrete is well known in the art of retaining wall blocks. The low slump concrete products industry produces many concrete block units in useful and practical shapes by placing a low slump concrete mixture into a mold that has been positioned atop a steel, plastic or wooden production pallet. After the mold has been filled, a head or top plunger with shoes is lowered atop the mixture within the mold to consolidate the mixture, with vibration, sufficiently for demolding. The top of this newly formed concrete block unit can have an irregular top surface since the head or top plunger can have shoes manufactured to impose this irregular surface atop the block unit. The multiple sides of the block unit are generally vertical although they can take on many contours along and around their perimeter. The bottom of the newly formed block unit is flat along its horizontal surface, although the unit may have internal cavities. The bottom of the unit remains flat because this is the area that was in contact with the flat production pallet. After the unit has been demolded, it remains atop the production pallet to undergo curing. After curing, the unit is removed from the production pallet for possible splitting into multiple finished blocks before being consolidated in a cube for inventorying.
A method of adding a contour to the bottom of a green uncured low slump concrete retaining wall block that has been formed in a single mold is known. A mold is placed atop a production conveyor belt before the concrete mixture is introduced. Next, a single or multiple horizontal core bar or bars are positioned within the mold atop the production belt continuous over the bottom of the mold from front to back. Then the mold is filled with a low slump concrete mixture and the head or top plunger with shoes is lowered into the top of the mold for consolidation. After this function, the core bar or bars are extracted from the mold leaving a contoured void from front to back of the bottom of the unit atop the production belt. Lastly, the block is demolded and cured.
One major drawback of the foregoing conventional method is the additional production time required to install the core bar or bars into the mold before adding the concrete mixture and to extract them after mixture consolidation but before demolding the block. Also, the extent of contouring along the bottom of the block is limited to the ability of the resultant block unit to sustain structural integrity due to the plastic green uncured state of the vertical sidewalls positioned overtop and therefore spanning a contoured void.